The second peak at \(D_n4000\sim 1.5\)  corresponds to the
dominant AGN population shown in Figure REF .
This peak was not found in [1]}, because they only
focused on star burst galaxies and their sample contained
only few galaxies with \(D_n4000\ge 1.5\) .
[2]} studied the H\(\delta \)  absorption
lines of AGN host galaxies and found that a significant fraction
of them have experienced a star burst phase within the past
1-2 Gyrs. Thus, the host galaxies of AGNs in this peak may
have also been triggered by a processes associated with a star burst.
However, since the life time for AGN activities is believed to be less
than \(10^8\)  years[3]}, [4]}, [5]}, the observed AGNs in this peak
cannot be directly related to the star bursts that happened 1 to 2
Gyrs ago. We will come back to the implications of this results later.
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